Differential current amplifier

ABSTRACT

A differential amplifier circuit wherein one collector of the multicollector of each of first, second and third inverse NPN transistors is connected to a base of the corresponding transistor; the first and second transistors are used as differential input transistors; the other collector of each of the first and second transistors is connected to a PNP transistor serving as a load current source; and an output is derived through the third transistor connected to the second transistor.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

This invention relates to a current comparison type differential amplifier. More particularly, it relates to a differential amplifier employing current-mirror circuits which are composed of NPN transistors that are operated in the inverse mode (hereinbelow, simply termed "inverse NPN transistors") or which are composed of integrated injection logic (hereinafter, abbreviated to "I² L").

(2) Description of the Prior Art

Differential amplifiers which have heretofore been known are circuits of the voltage comparison type which amplifies the voltage difference between two input signals. FIG. 1A of the accompanying drawings shows a prior-art differential amplifier.

As shown in the figure, the emitters of a pair of transistors Q₁ and Q₂ are connected in common and connected to a constant current source I. Since the constant current source I has a very high impedance, the respective transistors Q₁ and Q₂ effect the emitter-follower operation and their input impedances become very high. If the transistors Q₁ and Q₂ and loads R₁ and R₂ are chosen to be substantially identical respectively and input voltages V_(I1) and V_(I2) are equal voltages, currents to flow through the respective transistors Q₁ and Q₂ will become equal. If the input voltage V_(I1) is greater than the input voltage V_(I2), the current of the transistor Q₁ will become greater than that of the transistor Q₂. Since both the transistors have the emitters coupled and connected to the constant current source, the current increment of the transistor Q₁ and the current decrement of the transistor Q₂ become equal, and a voltage increment which is proportional to the current decrement of the transistor Q₂ appears in an output voltage V_(out).

In this manner, the prior-art differential amplifier is such that since the input impedances are very high, the input currents are small, the output being provided by comparing the input voltages.

With the prior-art differential amplifier, the respective transistors and resistors need to be fabricated in an isolated manner within an integrated circuit. Usually, also the constant current source in FIG. 1A is an NPN transistor. An example of a layout pattern in the case of the differential amplifier of FIG. 1A within the integrated circuit is shown in FIG. 1B. As illustrated in FIG. 1B, the transistors Q₁ and Q₂ constituting the differential pair, the transistor Q₃ for the constant current source, and the resistors R₁ and R₂ must be formed in island regions 11 respectively enclosed with an isolation region 10. Therefore, the area which the differential amplifier occupies in the integrated circuit becomes large.

In the case where, as an application of the differential amplifier, a photocell is used for the input of the voltage comparison type differential amplifier, the circuit arrangement is as shown in FIG. 1C. Inputs (+) and (-) in FIG. 1C correspond to the inputs V_(I1) and V_(I2) in FIG. 1A. D₁ designates a diode being the photocell, which provides a current proportional to a quantity of light. D₂ designates a diode for converting into a voltage the current produced by the diode D₁.

When the optical input is feeble, the current of the diode D₁ naturally becomes very small, and it becomes 100 pA--several hundreds pA or so in some cases. Even under such a state, the differential amplifier indicated at A needs to effect a precise amplification in response to the input signal. The diode D₁ is connected in parallel between the input of the differential amplifier and the earth side. Therefore, if the current produced by the diode D₁ flows into the input side of the differential amplifier, precise amplification will be impossible. For this reason, a very great value is required for the impedance of the differential amplifier, and the specification of the input current needs to be several tens pA or less.

In the case where the prior-art differential amplifier is used together with an I² L, the signal levels of both the circuits are different, and hence, the output of the differential amplifier needs to be translated to the signal level of the I² L (or vice versa). In general, the output signal of the differential amplifier has a higher voltage level than the signal of the I² L. For the level translation, a level shift circuit is necessary besides the circuit shown in FIG. 1A, the circuit area increases still more.

SUMMARY OF THE INVENTION

This invention has for its object to make improvements in the prior-art differential amplifier including the problems described above.

An object of this invention is to provide a differential amplifier which has a simple circuit arrangement and which has a small circuit area in a semiconductor chip (IC chip or LSI chip).

Another object of this invention is to provide a differential amplifier which does not require a level translation for an I² L when it is used together with the I² L.

Still another object of this invention is to provide a current comparator type differential amplifier which can be constructed of only an I² L.

The differential amplifier of this invention is an amplifier wherein a plurality of current-mirror circuits are employed as current sources, they are combined to take the sum or difference of currents, and it is amplified.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic circuit diagram showing a prior-art differential amplifier.

FIG. 1B is a layout pattern view when the differential amplifier of FIG. 1A is formed in an integrated circuit.

FIG. 1C is a schematic circuit diagram when an output current of a photocell is used as an input of the differential amplifier of FIG. 1A.

FIG. 2A is a schematic circuit diagram showing a differential amplifier which is a first embodiment of this invention.

FIG. 2B is a layout pattern view of a transistor Q₁ when the differential amplifier of FIG. 2A is formed in an integrated circuit.

FIG. 2C is a schematic circuit diagram when a detection signal of a photocell is used as an input of the differential amplifier of FIG. 2A.

FIG. 3 is a schematic circuit diagram showing a differential amplifier which is a second embodiment of this invention.

FIG. 4 is a schematic circuit diagram showing a differential amplifier which is a third embodiment of this invention.

FIG. 5 is a schematic circuit diagram showing a differential amplifier of multiple inputs and outputs which is a fourth embodiment of this invention.

FIG. 6A shows a fifth embodiment of this invention, and is a schematic circuit diagram of a differential amplifier constructed of an I² L.

FIG. 6B shows a layout pattern view when the differential amplifier of FIG. 6A is formed in an integrated circuit.

FIGS. 7A and 7B are layout pattern views of integrated circuits for elucidating examples of the method of adjusting an injector current I_(inj2) within the differential amplifier of FIG. 6A.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

FIG. 2A shows a first embodiment of the differential amplifier of this invention. As seen from the figure, the differential amplifier of the present embodiment is made up of NPN transistors Q₁, Q₂ and Q₅ each of which has a plurality of collectors and is operated in the inverse mode (hereinbelow, simply termed "inverse NPN transistor") and PNP transistors Q₃ and Q₄. The inverse NPN transistors Q₁, Q₂ and Q₅ have the first collectors C₁₁, C₂₁ and C₅₁ of the multi-collectors connected to the bases thereof and construct current-mirror circuits between them and the second collectors C₁₂, C₂₂ and C₅₂, respectively. The NPN transistors Q₁ and Q₂ are transistors for differential inputs, and the PNP transistors Q₃ and Q₄ to serve as current sources of loads are connected to the second collectors C₁₂ and C₂₂ of the respective transistors. Also the PNP transistors Q₃ and Q₄ construct a current-mirror circuit. IN1 and IN2 indicate base terminals of the NPN transistors Q₁ and Q₂ respectively, the base terminals being input terminals. An output current is derived from a terminal OUT of the second collector C₅₂ of the NPN transistor Q₅ whose base is connected to the second collector C₂₂ of the NPN transistor Q₂. In FIG. 2A, V_(cc) indicates a power supply terminal.

In the circuit of FIG. 2A, an input current I₁ is applied to the input terminal IN1 and an input current I₂ is applied to the input terminal IN2. In the transistors Q₁ and Q₂, the ratio of a current to flow through the first collector connected to the base and a current to flow through the second collector is set at m. It is assumed that, in the transistor Q₅, the ratio of a current to flow through the first collector connected to the base and a current to flow through the second collector is set at n. At this time, the current of that second collector C₁₂ of the transistor Q₁ which is connected to the transistor Q₃ is m·I₁. Since the transistors Q₃ and Q₄ are also of the current-mirror circuit arrangement, the collector current of the transistor Q₄ becomes substantially m·I₁, too. On the other hand, the current of that second collector C₂₂ of the transistor Q₂ which is connected to the transistor Q₄ becomes m·I₂. Accordingly, a current to flow to the transistor Q₅ becomes m·(I₁ -I₂). An output current I_(OUT) of the transistor Q₅ is n times the current of the first collector C₅₁ connected to the base, so that it becomes:

    I.sub.OUT =m·n·(I.sub.1 -I.sub.2)        (1)

Accordingly, the current amplitude becomes:

    A.sub.I =I.sub.OUT /(I.sub.1 -I.sub.2)=m·n        (2)

As understood from Equation (1), the output current is obtained only when the input current I₁ is greater than the input current I₂. Accordingly, the present circuit is a differential amplifier circuit of the current comparison type.

The values m and n in Equation (2) can be arbitrarily set by varying the ratio between the area of the first collector connected to the base and the area of the second collector in the transistor Q₁, Q₂ or Q₃.

FIG. 2B shows an example of the layout pattern of the transistor Q₁. In the inverse NPN transistor, in case where the area of a base 21 is fixed and where the areas of collectors 22 and 23 are varied, the current gain is substantially proportional to the ratio between the collector area and the base area. In FIG. 2B, S_(C1) is let denote the area of the collector C₁₁ connected to the base (an interconnection 24 is connected with the base at 25). The area of the other collector C₁₂ is denoted by S_(C2). The base area is denoted by S_(B). Then, the current gains β₁ and β₂ of the respective collectors C₁₁ and C₁₂ become:

    β.sub.1 =k(S.sub.C1 /S.sub.B)                         (3)

    β.sub.2 =k(S.sub.C2 /S.sub.B)                         (4)

where k is a proportional constant. Accordingly, letting I_(B) denote the base current, currents I_(C1) and I_(C2) to flow through the respective collectors C₁₁ and C₁₂ become:

    I.sub.C1 =β.sub.1 I.sub.B =k(S.sub.C1 /S.sub.B)I.sub.B (5)

    I.sub.C2 =β.sub.2 I.sub.B =k(S.sub.C2 /S.sub.B)I.sub.B (6)

Therefore, the ratio of the currents of the collectors C₁₁ and C₁₂ becomes:

    I.sub.C2 /I.sub.C1 =S.sub.C2 /S.sub.C1 =m

The ratio of the currents is proportional to the ratio of the collector areas. Thus, the value m can be set by varying the collector areas as desired.

In case where a photocell is used for the current comparison type differential amplifier circuit shown in FIG. 2A, the photocell D₁ is incorporated in series with an input as shown in FIG. 2C. In FIG. 2C, the input (+) of the differential amplifier A₁ is the input IN2 in FIG. 2A, while an input (-) thereof is the input IN1. An output of the present circuit is connected to the input (-), and a reference current I_(ref) is applied to this point. Then, when the input (+) (the input IN2) increases, the output current increases. In the case where the photocell is incorporated in series with the input as shown in FIG. 2C, all the photo current generated in the photocell D₁ by an optical input flows to the amplifier, and this current is amplified. Therefore, the leakage current as in the voltage comparison type differential amplifier circuit shown in FIG. 1C does not need to be considered.

In this manner, the current comparison type differential amplifier circuit is very effective when combined with the photocell.

Embodiment 2

FIG. 3 shows a second embodiment of this invention. This embodiment is such that the current-mirror circuit of the PNP transistors in FIG. 2A is precisely constructed. In general, a PNP transistor has a low current gain. Therefore, a difference develops between the current flowing on the collector side of the transistor Q₃ and the current flowing on the collector side of the transistor Q₄. In order to make the difference small, a transistor Q₆ is added. When the base of the transistor Q₃ is connected to the collector thereof as in the foregoing embodiment, the current at this point becomes the sum of the collector current and the base currents of the transistors Q₃ and Q₄. On the other hand, only the collector current flows on the collector side of the transistor Q₄. Accordingly, the currents on the collector sides of the transistors Q₃ and Q₄ have a difference corresponding to the base current component. When the transistor Q₆ is added as in the present embodiment, the base currents of the transistors Q₃ and Q₄ become the emitter current of the transistor Q₆, and the current on the collector side of the transistor Q₃ becomes the sum of the collector current of the transistor Q₃ and the base current of the transistor Q₆. Since the base current of the transistor Q₆ becomes approximately 1/(current gain) of the emitter current, the difference of the currents on the collector sides of the transistors Q₃ and Q₄ is very small.

Embodiment 3

FIG. 4 is a diagram showing a third embodiment of the differential amplifier of this invention.

This embodiment shown in FIG. 4 illustrates a method for applying negative feedback. A third collector C₅₃ is disposed in the NPN transistor Q₅ in FIG. 2A and is connected to the base of the NPN transistor Q₁, whereby the negative feedback can be applied. Letting l denote the ratio between the current sinking capability of the third collector C₅₃ connected to the base of the NPN transistor Q₁ and the current sinking capability of the second collector C₅₂ serving as the output terminal OUT, the current amplitude of the present circuit becomes: ##EQU1## In this manner, the differential amplifier circuit according to this invention can freely set the quantity of negative feedback by varying the areas of the collectors of the NPN transistor.

Embodiment 4

FIG. 5 shows a fourth embodiment of the differential amplifier according to this invention. The differential amplifier shown in FIG. 5 teaches an arrangement which has multiple inputs and outputs. NPN transistors Q₂ ', Q₂ ", Q₅ ' and Q₅ " and PNP transistors Q₄ ' and Q₄ " are added to the differential amplifier shown in FIG. 2A. An input current at the input terminal IN1 and input currents at input terminals IN2, IN3 and IN4 are compared, and output currents are derived from output terminals OUT1, OUT2 and OUT3.

Embodiment 5

FIG. 6A shows a fifth embodiment of the differential amplifier of this invention. The differential amplifier shown in FIG. 6A teaches a construction which employs I² Ls. In the figure, Q₂₁, Q₂₂, Q₂₃ and Q₂₄ indicate lateral PNP transistors of the I² Ls, and they are used as common base circuits. Q₁₁, Q₁₂, Q₁₃ and Q₁₄ indicate inverse NPN transistors of the I² Ls, and they are of the current-mirror construction. The transistors Q₁₁ and Q₂₃, the transistors Q₁₃ and Q₂₂, the transistors Q₁₂ and Q₂₄ and the transistors Q₁₄ and Q₂₁ constitute the I² Ls, respectively.

The differential amplifier in FIG. 6A amplifies a current which is proportional to the difference between an input applied to an input terminal IN1 being the base terminal of the inverse NPN transistor Q₁₁ (current I₁ drawn out from the base of the transistor Q₁₁) and an input applied to an input terminal IN2 being the base terminal of the inverse NPN transistor Q₁₂ (current I₂ drawn out from the base of the transistor Q₁₂), and provides the amplified current from an output terminal OUT being the second collector terminal C₁₃₂ of the inverse NPN transistor Q₁₃. Supposing that the areas of the first and second collectors of the respective transistors Q₁₁, Q₁₂, Q₁₃ and Q₁₄ are equal and that injector current I_(inj1) =I_(inj3), then the sinking current of the second collector C₁₄₂ of the inverse NPN transistor Q₁₄ is equal to the current I₁, the sinking current of the second collector C₁₂₂ of the inverse NPN transistor Q₁₂ is equal to (I_(inj4) -I₂), and the sum of both these currents becomes (I_(inj4) -I₂ +I₁). At a node H, an injector current I_(inj2) and the sum (I_(inj4) -I₂ +I₁) are compared. The difference of both these currents, {I_(inj2) -(I_(inj4) -I₂ +I₁)} flows into the base of the inverse NPN transistor Q₁₃, and it is provided from the terminal OUT. Assuming here that injector current I_(inj4) =injector current I_(inj2), the output current becomes I₂ -I₁.

With the present circuit, the current amplitude can be increased by making the injector current I_(inj2) high or by making the areas of the second collectors C₁₁₂, C₁₂₂, C₁₃₂ and C₁₄₂ of the transistors Q₁₁, Q₁₂, Q₁₃ and Q₁₄ larger than the areas of the first collectors C₁₁₁, C₁₂₁, C₁₃₁ and C₁₄₁.

The layout pattern in an integrated circuit, of the differential amplifier of the I² L construction shown in FIG. 6A is illustrated in FIG. 6B. The pattern corresponds to a case where, in the circuit of FIG. 6A, the injector current I_(inj1) =injector current I_(inj2) =injector current I_(inj3) =injector current I_(inj4) and the areas of the respective collectors of the NPN transistors Q₁₁, Q₁₂, Q₁₃ and Q₁₄ are fixed (that is, m=n=1). Referring to FIG. 6B, numeral 60 designates an N-type semiconductor (such as Si) body, numeral 61 an injector area (P-type region serving as the emitters of the lateral PNP transistors), and numerals 62 and 62' P-type regions serving both as the collectors of the lateral PNP transistors and as the base of inverse NPN transistors. Further, areas 63 indicate N-type regions which serve as the collectors of the inverse NPN transistors. Dotted lines indicate electrode interconnections, and marks X represent contact holes into the respective regions.

In FIGS. 6A and 6B, the injector currents I_(inj1), I_(inj2), I_(inj3) and I_(inj4), i.e., the emitter currents of the lateral PNP transistors Q₂₁, Q₂₂, Q₂₃ and Q₂₄ can be arbitrarily set by adjusting the lengths of opposition to the injectors.

FIG. 7A is a view illustrative of a layout pattern in the case of adjusting the currents by making different the length L₁ by which the base regions 62 of the transistors Q₁₁, Q₁₂ and Q₁₄ face the injector region 61 and the length L₂ by which the base region 62' of the transistor Q₁₃ faces the injector region 61. In this case, the length L₂ is selected to be 1.5 times the length L₁. The injector current I_(inj2) and the injector currents I_(inj1), I_(inj3) and I_(inj4) flow according to this ratio.

Likewise, a method as illustrated in FIG. 7B is possible for the adjustment of the injector currents. In this method, the distances M₁ and M₂ at which the bases of the transistors Q₁₁, Q₁₂ and Q₁₄ and the base of the transistor Q₁₃ face the injectors respectively are made unequal. Thus, the injector current I_(inj2) can be made greater than the injector currents I_(inj1), I_(inj3) and I_(inj4).

The integrated injection logic (I² L) is described in, for example, the following literatures:

(1) K. Hart & A. Slob: Integrated Injection Logic--A New Approach to LSI, IEEE J. of SSC, sc-7, 5, pp. 346-351 (October 1972)

(2) H. H. Berger & S. K. Wiedmann: Merged Transistor Logic--A Low-Cost Bipolar Logic Concept, IEEE J. of SSC, sc-7, 5, pp. 340-346 (October 1972)

Embodiment 6

A circuit arrangement is also possible wherein, in the above embodiment, the collectors of the common-base PNP transistors are connected to the inputs IN1, IN2, . . . , and the emitters of the common-base PNP transistors are made inputs. In such a case, there is the advantage that the input impedance can be lowered because the PNP transistors are of the common-base type. These PNP transistors can be fabricated in quite the same way as that of the lateral PNP transistors of I² Ls.

The advantages of the differential amplifier of this invention will be listed below.

(1) The differential amplifier of this invention is a differential amplifier circuit of the current comparison type as illustrated in FIG. 2A.

(2) The differential amplifier of this invention has a simple circuit arrangement. In particular, the circuit shown in FIG. 6A can be constructed of only I² Ls, so that the circuit area becomes very small.

(3) The differential amplifier of this invention employs inverse NPN transistors used in I² Ls and common-base PNP transistors, and can be directly connected with ordinary I² Ls which effect logic operations.

(4) Being a differential amplifier of the current comparison type, the circuit. When used with a photocell as shown in FIG. 2C, the photocell can be incorporated in series with an input. Unlike the prior-art circuit, accordingly, the circuit of this invention does not need a high input impedance.

(5) The circuits in FIG. 2A, FIG. 4, FIG. 5 and FIG. 6A can operate with a supply voltage V_(cc) of approximately 0.7 V, and the amplifier in FIG. 3 can operate with a supply voltage V_(cc) of about 1.4 V.

(6) When inputs and outputs are made multiple as shown in FIG. 5, comparisons with currents of different levels can be carried out. This can be utilized as an A/D converter of the parallel comparison type.

(7) The quantity of feedback can be arbitrarily set by changing collector areas of an inverse NPN transistor.

The essentials of the construction of the differential amplifier of this invention will be listed below.

(1) A differential amplifier wherein a plurality of current sources are combined, and the sum or difference of currents is taken and amplified.

(2) A differential amplifier which employs current-mirror circuits as current sources.

(3) A differential amplifier wherein a circuit with one collector of an inverse PNP transistor connected to the base thereof is employed as a current-mirror circuit.

(4) A differential amplifier which employs the injector of an I² L circuit as a constant current source.

(5) A differential amplifier wherein, in a current-mirror circuit, the areas of the collectors of an inverse NPN transistor are made unequal to bestow a difference on the current sinking capabilities of the collectors.

(6) A differential amplifier wherein the lengths by which the bases of inverse NPN transistors face injectors are made unequal in order to make the current values of current sources unequal.

(7) A differential amplifier wherein common-base PNP transistors are disposed on the differential input sides, and the emitters of the PNP transistors are used as the inputs. 

What is claimed is:
 1. A differential current amplifier comprising:a first inverse NPN transistor which has first and second collectors, whose first collector is electrically connected to a base thereof and whose emitter is electrically grounded, a second inverse NPN transistor which has first and second collectors, whose first collector is electrically connected to a base thereof and whose emitter is electrically grounded, a third inverse NPN transistor which has first and second collectors, whose first collector is electrically connected to a base thereof and whose emitter is electrically grounded, a first input terminal which is the base terminal of said first inverse NPN transistor, a second input terminal which is the base terminal of said second inverse NPN transistor, an output terminal which is the second collector terminal of said third inverse NPN transistor, and a constant current circuit which is electrically connected to said second collector of said first inverse NPN transistor, said second collector of said second inverse NPN transistor and said base of said third inverse NPN transistor, a differentially amplified output current of input currents at said first and second input terminals being provided from said second collector of said third inverse NPN transistor as forms said output terminals, and wherein said constant current circuit comprises: a first PNP transistor whose collector is electrically connected to said second collector of said first inverse NPN transistor and whose emitter is electrically connected to a power supply, and a second PNP transistor whose collector is electrically connected to said second collector of said second inverse NPN transistor and a base of said third inverse NPN transistor, whose base is electrically connected to said base of said first PNP transistor and whose emitter is electrically connected to said power supply.
 2. A differential current amplifier according to claim 1, further comprising a fourth inverse NPN transistor which has first and second collectors, whose first collector is electrically connected to a base thereof and whose emitter is electrically grounded, said base and said second collector of said fourth inverse NPN transistor being electrically connected to said second collector of said first NPN transistor and said collector of said second PNP transistor respectively.
 3. A differential current amplifier according to claim 2, wherein:said constant current circuit comprises first, second, third and fourth PNP transistors whose emitters are electrically connected to a power supply and whose bases are electrically grounded, said collector of said first PNP transistor is electrically connected to said second collector of said first inverse NPN transistor, said collector of said second PNP transistor is electrically connected to said second collectors of said second and fourth inverse NPN transistors, said collector of said third PNP transistor is electrically connected to said base of said first inverse NPN transistor, and said collector of said fourth PNP transistor is electrically connected to said base of said second inverse NPN transistor.
 4. A differential current amplifier according to claim 3, wherein said first inverse NPN transistor and said third PNP transistor, said second inverse NPN transistor and said fourth PNP transistor, said third inverse NPN transistor and said second PNP transistor, and said fourth inverse NPN transistor and said first PNP transistor constitute first, second, third, and fourth integrated injection logics, respectively.
 5. A differential current amplifier according to claim 4, wherein injector current values of said first and fourth integrated injection logics are equal.
 6. A differential current amplifier according to claim 5, wherein an injector current value of said third integrated injection logic is not smaller than an injector current value of said second integrated injection logic.
 7. A differential current amplifier according to claim 2, 3, 4, 5 or 6, wherein an area of said second collector is larger than that of said first collector in at least one of said first, second, third and fourth inverse NPN transistors.
 8. A differential current amplifier comprising:a first inverse NPN transistor which has first and second collectors, whose first collector is electrically connected to a base thereof and whose emitter is electrically grounded, a second inverse NPN transistor which has first and second collectors, whose first collector is electrically connected to a base thereof and whose emitter is electrically grounded, a third inverse NPN transistor which has first and second collectors, whose first collector is electrically connected to a base thereof and whose emitter is electrically grounded, a first input terminal which is the base terminal of said first inverse NPN transistor, a second input terminal which is the base terminal of said second inverse NPN transistor, an output terminal which is the second collector terminal of said third inverse NPN transistor, and a constant current circuit which is electrically connected to said second collector of said first inverse NPN transistor, said second collector of said second inverse NPN transistor and said base of said third inverse NPN transistor, a differentially amplified output current of input currents at said first and second input terminals being provided from said second collector of said third inverse NPN transistor as forms said output terminal, wherein said third inverse NPN transistor has a third collector which is electrically connected to said base of said first inverse NPN transistor.
 9. A differential current amplifier according to claim 1 or 8, wherein said collector and said base of said first PNP transistor are connected.
 10. A differential current amplifier according to claim 9, wherein said collector and said base of said first PNP transistor are connected through a third PNP transistor whose collector is electrically grounded and whose base and emitter are electrically connected to said collector and base of said first PNP transistor respectively.
 11. A differential current amplifier comprising:a first inverse NPN transistor which has first and second collectors, whose first collector is electrically connected to a base thereof and whose emitter is electrically grounded, a second inverse NPN transistor which has first and second collectors, whose first collector is electrically connected to a base thereof and whose emitter is electrically grounded, a third inverse NPN transistor which has first and second collectors, whose first collector is electrically connected to a base thereof and whose emitter is electrically grounded, a first PNP transistor whose collector is electrically connected to said second collector of said first inverse NPN transistor and whose emitter is electrically connected to a power supply, a second PNP transistor whose collector is electrically connected to said second collector of said second inverse NPN transistor, whose base is electrically connected to a base of said first PNP transistor, and whose emitter is electrically connected to said power supply, means for supplying the base of said third inverse NPN transistor with a differential current which is equal to or less than a difference between a collector current I_(c0) of said second PNP transistor and a current I_(c2) of the second collector of said second inverse NPN transistor and which includes a difference between the current I_(c1) of the second collector of said first inverse NPN transistor and the current I_(c2), a first input terminal which is the base terminal of said first inverse NPN transistor, a second input terminal which is the base terminal of said second inverse NPN transistor, and an output terminal which is the second collecor terminal of said third inverse NPN transistor, a differentially amplified output current of input currents at said first and second input terminals being provided from said second collector of said third inverse NPN transistor as forms said output terminal.
 12. A differential current amplifier according to claim 11, wherein the collector of said first PNP transistor is electrically connected to the base thereof so that the current I_(c0) becomes substantially the current I_(c1),and said differential current is a difference between the current I_(c1) and the current I_(c2).
 13. A differential amplifier according to claim 11 further comprising:a fourth inverse NPN transistor which has first and second collectors, whose first collector is electrically connected to a base thereof and whose emitter is electrically grounded, said base and said second collector of said fourth inverse NPN transistor being electrically connected to said second collector of said first NPN transistor and said collector of said second PNP transistor respectively, third and fourth PNP transistors whose emitters are electrically connected to said power supply and whose bases are electrically connected to the bases of said first and second PNP transistors, and wherein the bases of said first, second, third and fourth PNP transistors are electrically grounded, a collector of said third PNP transistor is electrically connected to the base of said first inverse NPN transistor, and a collector of said fourth PNP transistor is electrically connected to the base of said second inverse NPN transistor.
 14. A differential current amplifier according to claim 13, wherein an area of said second collector is larger than that of said first collector in at least one of said first, second and third inverse NPN transistors.
 15. A differential current amplifier according to claim 12, 13, 14, 2, 3 or 4, wherein collectors of fifth and sixth common-base PNP transistors whose emitters form input terminals are respectively connected to said first and second input terminals. 